1. Field of the Invention
The present invention relates to optical switches used to connect the optical fibers in an optical cable to a Remote Fiber Test System (RFTS), when the optical fibers are being laid, repaired or otherwise altered. More particularly, the present invention relates to an optical switch system that selectively directs optical test signals to optical fibers that are part of a fiber administration system when the integrity of those optical fibers are in question.
2. Description of the Prior Art
There are many applications that utilize an optical fiber network to establish optical communications between a host digital terminal (HDT) at a central office and an optical network unit (ONU) at a remote location. Since a central office serves as the point of origin for the optical fibers in the optical fiber network, fiber administration systems are typically used at the central office to manage the flow of optical signals as they are directed to the various ONUs along the different optical fibers in the network.
In many fiber administration systems, as the optical fibers in a network enter the central office, they are directed into an optical distribution frame where the individual optical fibers are terminated in an organized manner. Such fiber administration systems are exemplified by the LGX.RTM. fiber administration system which is currently manufactured by Lucent Technologies of Murray Hill, N.J., the assignee herein. In such fiber administration systems, the optical distribution frames used at the central office are typically large structures that are arranged in parallel rows. Each optical distribution frame is commonly mounted between the floor and ceiling and only a few feet separate each row of frames.
Each optical distribution frame located at the central office typically defines a plurality of bays, wherein each bay houses several fiber distribution shelves. On each of the fiber distribution shelves are optical couplings that receive the ends of all of the individual optical fibers that enter the central office and are contained within the optical fiber network. By terminating each optical fiber at a coupling on one of the different fiber distribution shelves, the location of each optical fiber becomes known within the overall assembly. Once terminated at a known address on one of the fiber distribution shelves, each optical fiber can be selectively coupled to an HDT or a variety of other pieces of optical equipment located at the central office. As a result, the optical signals sent along each optical fiber can be selectively controlled.
As an optical fiber cable is connected between the optical distribution frame at the central office and the various ONUs at remote locations, the many optical fibers contained within the fiber cable must be spliced at different points along the path. For example, the optical fibers in an optical fiber cable are typically spliced to connector fibers at the outside cable entrance facility (OCEF), where the optical fiber cable enters the central office. The connector fibers extend through conduits in the central office and lead to the optical fiber distribution frame. The various optical fibers are also commonly spliced at one or more manhole locations in between the central office and a grouping of ONUs. As such, most every optical fiber is spliced in more than one location in between the central office and each ONU.
When an optical fiber cable is newly laid, repaired, sliced or otherwise altered, it is important to check the optical integrity in between the central office and each ONU. As a result, each time an optical fiber cable is altered, the integrity of the overall optical pathway must be tested. In many applications, an optical cable exiting the central office contains several different optical ribbons. Each of the ribbons contains a plurality of individual optical fibers, for example, twelve (12) individual optical fibers. When an optical cable is spliced, the cable is cut open and each of the optical ribbons contained within that cable are spliced individually. As such, when one optical ribbon is spliced to another, several different individual optical fibers are being spliced during that operation. If any one of the optical fibers in the optical ribbon fails to splice properly, either that ribbon or the entire optical cable must be cut and re-spliced.
In the prior art, the testing of the integrity and quality of a splice is performed after each splice is completed. Traditionally, such a testing procedure required at least two individuals. One person is the splicer who splices the cable in a manhole or at some other remote location. The second person would be in charge of the test equipment at the central office. The two people would be in communications with one another. When the splice of a single optical ribbon was complete, a test would be initiated. As the test was performed, the integrity of each of the optical pathways could be tested.
In the past, the various optical fibers in a ribbon would be connected to test equipment using an optical switching device such as that described in U.S. patent application Ser. No. 08/709,943, to Pimpinella et al., entitled Optical Switching Apparatus And Method For Use In The Construction Mode Testing Of A Modular Fiber Administration System, the disclosure of which is herein incorporated into this specification by reference. The purpose of such optical testing devices is to connect a single optical testing device to multiple optical fibers and then to switch the testing device to the different optical fibers while testing is being performed. Such optical testing devices therefore have a single optical input that connects to the testing equipment and multiple optical leads that connect to the various optical fibers.
In the central office the space available on any one fiber distribution shelf is very limited. A typical optical cable contains at least seventy two (72) optical fibers. For test equipment to be attached to the optical fibers, at least seventy two separate leads have to be connected between the connector ports on the fiber distribution shelf and the equipment being used to test the optical fibers. The organization of seventy two different leads is very difficult. Often the leads become tangled and unmanageable. Consequently, test equipment is commonly coupled to just one optical ribbon at a time. An optical ribbon typically contains twelve optical fibers. As a result, the person in the central office need only connect twelve leads before testing can occur. After the test is completed, the person and the person at the central office remove the leads from the optical fibers of the first optical ribbon and reconnect those leads to the optical fibers of the next optical ribbon to be tested. As such, in the prior art, such testing is often a time and labor-intensive undertaking.
A need, therefore, exists in the art for an optical switching device that is capable of connecting to all the optical fibers contained in an optical cable at the same time and in a highly organized and time efficient manner, thereby eliminating the step of having to change test equipment from one optical ribbon to another in a testing cycle.